The result of (nixos-install && nixos-enter) lacks the /tmp directory

[pvgoran]

Issue description

I have a process that creates a "clean" NixOS filesystem tree for later usage. First, I create the minimal NixOS configuration files at $ROOT/etc/nixos, then I run:

nixos-install --no-bootloader --no-root-passwd --root "$ROOT"
nixos-enter --root "$ROOT" -- true

(Before 18.03, it worked without nixos-enter. I'm not very happy that now I need an additional step, and I'll probably create a separate issue about this. But I can understand that nixos-install creates a minimal installation and nixos-enter activates it.)

I expect to be able to chroot into the resulting filesystem tree and have a fully-working NixOS system. However, these steps don't create the /tmp directory, which prevents nixos-rebuild from working:

[root@nixos-seed:/]# nixos-rebuild dry-build
mktemp: failed to create directory via template ‘/tmp/nixos-rebuild.XXXXXX’: No such file or directory

Steps to reproduce

Build the NixOS tree:

mkdir seed
mkdir -p seed/etc/nixos
cat >seed/etc/nixos/configuration.nix <<END
{ config, pkgs, ... }:
{
  boot.loader.grub.enable = true;
  boot.loader.grub.version = 2;
  boot.loader.grub.device = "/dev/dummy";

  fileSystems."/" =
    { device = "/dev/dummy";
      fsType = "ext4";
    };
}
END
nixos-install --no-bootloader --no-root-passwd --root $(realpath seed)
nixos-enter --root $(realpath seed) -- true

Then try to work in it:

nixos-enter --root $(realpath seed) -- nixos-rebuild dry-build

Technical details

• system: "x86_64-linux"
• host os: Linux 4.14.34, NixOS, 18.03.132021.c0c5571ec1a (Impala)
• multi-user?: yes
• sandbox: no
• version: nix-env (Nix) 2.0
• channels(paul): ""
• channels(root): "nixos-18.03.132021.c0c5571ec1a"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs

[CMCDragonkai]

That is pretty cool, how do you switch to the seed later? Is the seed mounted from a remote machine?

[pvgoran]

@CMCDragonkai The seed is packed into a squashfs image which is transferred to the target system. Then a script is run which mounts the image, chroots into it, rsyncs the seed onto the target system's root, and finally chroots the second time into the root to run nixos-rebuild boot.

[chkno]

For concreteness: A fix for this problem would cause this test to pass, or at least fail for a different reason. Currently this test fails with this output:

$ nix-build nixos/tests/installer.nix -A simple
...
Can build things in the installed environment
machine: must succeed: nixos-enter -- nix-build ...
machine # setting up /etc...
machine # error: getting status of '/tmp': No such file or directory
machine: output:
error: command `nixos-enter -- nix-build ... failed (exit code 1)

Adding mkdir --mode 1777 /mnt/tmp allows the test to continue.

---

It looks like /tmp is normally created by the systemd-tmpfiles-setup systemd service which runs at boot. Starting up systemd seems out-of-scope for nixos-enter. Perhaps it should just run systemd-tmpfiles --create --remove --exclude-prefix=/dev like switch-to-configuration.pl does.

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[pvgoran]

This issue is still relevant.

[louwers]

Still a problem when just using nixos-install!

[Mikilio]

This issue should be reopened as it is the root cause of other problems like #73404. The line added with the fix (#80769) of this issue seems to fail on many uses of nixos-install.sh which calls nixos-enter.sh when attempting to install the bootloader. The error given is not being able to find the command systemd-tmpfiles when using chroot at this stage. Does anyone know why systemd-tmpfiles was supposed to be in PATH here in the first place? I can not understand how this fix used to work before.

[nh2]

Reopening based on reports above.

[Mikilio]

Regarding my previous comment, I have confirmed that systemd-tmpfiles is indeed not in the PATH and one should not assume that it would be there. That is because the dependency of nixos-enter on systemd hasn't been declared in tools.nix where it should be. The fix should be easy, so I will submit a pull request.

[ncfavier]

Fixed by #199425